<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var n1 = +prompt('第一个数字');
        var n2 = +prompt('第二个数字');

        alert(`${ n1 } + ${ n2 } = ${ n1 + n2 }`);
    </script>
</body>
</html>